Conventionally, as a power conversion circuit having a configuration in which a freewheel diode is connected in inverse parallel with a switching element in a main circuit, there has been proposed a power conversion circuit in which a loss caused as the result of the reverse recovery current of the freewheel diode being turned on is reduced. Such a power conversion system having a power conversion circuit is disclosed in, for example, Japanese Patent Laid-Open No. 2006-141167 (Patent Document 1) and Japanese Patent Laid-Open No. 2006-141168 (Patent Document 2).
However, in such a conventional power conversion system as disclosed in Patent Document 1 or Patent Document 2, a large current of a main circuit temporarily flows into an additional circuit at the time of reverse recovery of the freewheel diode, thus causing an increase in the scale of the additional circuit. Consequently, the conventional power conversion system has a problem that a relatively large-capacity auxiliary power supply having a relatively large capacity alkalis required. In addition, there arises the need for a logic circuit for generating the gate pulse signal of a switching element used in the additional circuit. Accordingly, the conventional power conversion system provides a problem that the circuitry thereof becomes complicated. Furthermore, the switching element used in the additional circuit needs to be enabled during a dead-time period of the main circuit. This causes timing constraints to tighten and, therefore, makes the power conversion system unsuited for high-speed switching.